LTE Overview

ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

ITU/BDT Arab ITU/BDT Arab Regional Workshop on Workshop on “4G Wireless Systems” LTE Technology

Session 3 : LTE Overview – Design Targets and Multiple Access Technologies and Multiple Access Technologies Speakers

M. Lazhar BELHOUCHET M Hakim EBDELLI M. Hakim EBDELLI

Date

27 – 29 January 2010

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LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Agenda • • • • • • •

Standardization Motivation for LTE Motivation for LTE LTE performance requirements LTE challenges LTE challenges LTE/SAE Key Features LTE technology basics LTE technology Air Interface Protocols

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LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Standardization • LTE is the latest standard in the mobile network technology p y / / tree that previously realized the GSM/EDGE and UMTS/HSxPA network technologies that now account for over 85% of all mobile subscribers. LTE will ensure 3GPP’s competitive edge over other cellular technologies.

• 3GPP work on the Evolution of the 3G Mobile System started in November 2004 in November 2004.

• Specifications scheduled finalized by the end of December 2009.

• Currently, standardization in progress in the form of Rel‐9 and Rel‐10.

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LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Motivation for LTE • Need for higher data rates and greater spectral efficiency – Can be achieved with HSDPA/HSUPA / – and/or new air interface defined by 3GPP LTE

• Need for Packet Switched optimized system – Evolve UMTS towards packet only system

• Need for high quality of services – Use of licensed frequencies to guarantee quality of services – Always‐on experience (reduce control plane latency significantly) – Reduce round trip delay R d dt i d l

• Need for cheaper infrastructure – Simplify architecture, reduce number of network elements Simplify architecture reduce number of network elements 4

LTE Overview

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LTE performance requirements • Data Rate: – Instantaneous downlink peak data rate of 100Mbit/s in a 20MHz p / downlink spectrum (i.e. 5 bit/s/Hz) – Instantaneous uplink peak data rate of 50Mbit/s in a 20MHz uplink spectrum (i e 2 5 bit/s/Hz) spectrum (i.e. 2.5 bit/s/Hz)

• Cell range – 5 km ‐ 5 km ‐ optimal size optimal size – 30km sizes with reasonable performance – up to 100 km cell sizes supported with acceptable performance

• Cell capacity – up to 200 active users per cell(5 MHz) (i.e., 200 active data clients) 5

LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

LTE performance requirements – Cont.

• Mobility – Optimized for low mobility(0‐15km/h) but supports high speed p y( / ) pp g p

• Latency – user plane < 5ms – control plane < 50 ms

• • • • •

Improved spectrum efficiency Improved broadcasting IP‐optimized Scalable bandwidth of 20, 15, 10, 5, 3 and 1.4MHz Co‐existence with legacy standards 6

LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

The way to LTE: 3 main 3G limitations 1.The maximum bit rates still are factor of 20 and more behind the y / current state of the systems like 802.11n and 802.16e/m.

2.The latency of user plane traffic (UMTS: >30 ms) and of resource assignment procedures (UMTS: >100 assignment procedures (UMTS: 100 ms) is too big to handle traffic ms) is too big to handle traffic with high bit rate variance efficiently.

3.The terminal complexity for WCDMA or MC 3 The terminal complexity for WCDMA or MC‐CDMA CDMA systems is quite systems is quite high, making equipment expensive, resulting in poor performing implementations of receivers and inhibiting the implementation of other performance enhancements.

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LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

LTE Overview – Design Targets LTE Overview Design Targets and Multiple Access Technologies and Multiple Access Technologies

LTE CHALLENGES

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LTE Overview

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What are the LTE challenges?

The Users’ expectation…

Best price, transparent flat rate F ll IInternet Full t t Multimedia

..leads to the operator’s challenges reduce cost per bit provide id hi high hd data t rate t provide low latency

User experience will have an impact on ARPU

Price per Mbyte has to be reduced to remain profitable

Throughput

Latency Cost per MByte

HSPA

LTE

HSPA

LTE UMTS

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LTE Overview

HSPA

I-HSPA

LTE

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Comparison of Throughput and Latency • Peak data rates around 300Mbps/80 Mbps • Low latency 10-20 ms

350 300

Mbps

250

Enhanced consumer experience: drives subscriber uptake allow for new applications provide additional revenue streams Latency (Rountrip delay) delay)*

Max. peak data rate GSM/ EDGE Downlink Uplink

HSPA Rel6 R l6

200

HSPAevo (Rel8)

150 100

LTE

50

min max

0 Evolved HSPA (Rel. 7/8, 2x2 MIMO)

HSPA R6

LTE 2x20 MHz (2x2 MIMO)

LTE 2x20 MHz (4x4 MIMO)

0

20

40

60

80

100

120

140

160

180

200 ms

DSL ((~20-50 ms,, depending p g on operator) p ) * Server near RAN

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Scalable Bandwidth Scalable Bandwidth

• Scalable bandwidth of 1.4 – 20 MHz

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Easy to E t introduce i t d on any ffrequency band: b d Frequency Refarming (Cost efficient deployment on lower frequency q y bands supported) pp )

LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Increased Spectral Efficiency

bps/Hz//cell

• • 2.0 18 1.8 1.6 1.4 1.2 1.0 0.8 0.6 04 0.4 0.2 0.0

All cases assume 2‐antenna terminal reception HSPA R7, WiMAX and LTE assume 2‐antenna BTS transmission (2x2 MIMO) Downlink Uplink

HSPA R6 12

ITU contribution from WiMAX Forum shows downlink 1.3 and uplink 0.8 bps/Hz/cell

HSPA R6 +

HSPA R7

WiMAX

LTE Overview

LTE R8

Reference: - HSPA R6 and LTE R8 from 3GPP R1-071960 - HSPA R6 equalizer from 3GPP R1-063335 - HSPA R7 and WiMAX from NSN/Nokia simulations

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Reduced Network Complexity Flat Architecture: 2 nodes architecture IP based Interfaces

Flat, scalable IP based architecture

Flat, IP based architecture Access

Core

Flat networks are characterized by fewer network elements, lower latency, greater flexibility and lower operation p cost Evolved Node B

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Control

MM

IM

HLR/H

E

S

SS

I t Internet t

GateWay

LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

LTE Overview – Design Targets LTE Overview Design Targets and Multiple Access Technologies and Multiple Access Technologies

LTE/SAE KEY FEATURES

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LTE Overview

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LTE/SAE Key Features – Overview EPS ( Evolved Packet System ) / SAE ( System Architecture Evolution ) / LTE ( Long Term Evolution ) EUTRAN ( Evolved UTRAN )

EPC ( Evolved Packet Core )

IP Network

IP Network

IP Network OFDMA/SC-FDMA

Evolved E l d Node N d B / No RNC

MIMO ( beam-forming/ spatial multiplexing)

IP Transport Layer

HARQ

UL/DL resource scheduling

Scalable bandwidth (1.4, 3, 5, 10, .. 20 MHz)

PS Domain only, No CS Domain IP Transport Layer QoS Aware 3GPP (GTP) or IETF (MIPv6) Prepared for Non-3GPP Access

QoS Aware Self Configuration

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LTE Overview

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LTE/SAE Key Features • Evolved NodeB – No RNC is provided anymore – The evolved Node Bs take over all radio management functionality.

– This will make radio management faster and hopefully the network architecture simpler architecture simpler

• IP transport layer – EUTRAN exclusively uses IP as transport layer y p y

• UL/DL resource scheduling – In UMTS physical resources are either shared or dedicated – Evolved Node B handles all physical resource via a scheduler and assigns them dynamically to users and channels – This provides greater flexibility than the older system This provides greater flexibility than the older system 16

LTE Overview

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LTE/SAE Key Features – Cont.

• Frequency Domain Scheduling :

Carrier bandwidth

– Frequency domain scheduling uses those resource blocks that are bl k th t not faded – Not possible in CDMA Not possible in CDMA based system

Resource block

Transmit on those resource blocks that are not faded 17

LTE Overview

Frequency

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LTE/SAE Key Features – Cont.

• HARQ – Hybrid Automatic Retransmission on reQuest on reQuest – HARQ has already been used for HSDPA and HSUPA. – HARQ especially increases the performance (delay and throughput) for cell edge users. g p ) g – HARQ simply implements a retransmission protocol on layer 1/2 that allows to send 1/2 that allows to send retransmitted blocks with different coding than the 1st one.

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LTE Overview

HARQ Hybrid Automatic Repeat Request

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LTE/SAE Key Features – Cont.

• QoS awareness – The scheduler must handle and distinguish different quality of service g q y classes – Otherwise real time services would not be possible via EUTRAN – The system provides the possibility for differentiated service

• Self configuration – Currently under investigation C tl d i ti ti – Possibility to let Evolved Node Bs configure themselves

• It It will not completely substitute the manual configuration and will not completely substitute the manual configuration and optimization.

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LTE Overview

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LTE/SAE Key Features – Cont.

• Packet Switched Domain only – No No circuit switched domain is provided circuit switched domain is provided – If CS applications are required, they must be implemented via IP via IP

• Non‐3GPP access – Th The EPC will be prepared also to be used by non‐3GPP EPC ill b d l t b db 3GPP access networks (e.g. LAN, WLAN, WiMAX, etc.)

– This will provide true convergence of different packet radio This will provide true convergence of different packet radio access system 20

LTE Overview

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LTE/SAE Key Features – Cont.

• MIMO – Multiple Multiple Input Multiple Output Input Multiple Output – LTE will support MIMO as an option, – It describes the possibility to have multiple transmitter and It describes the possibility to have multiple transmitter and receiver antennas in a system.

– Up to four antennas can be used by a single LTE cell (gain: Up to four antennas can be used by a single LTE cell (gain: spatial multiplexing) – MIMO is considered to be the core technology to increase MIMO is considered to be the core technology to increase spectral efficiency.

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LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

LTE Overview – Design Targets LTE Overview Design Targets and Multiple Access Technologies and Multiple Access Technologies

LTE TECHNOLOGY BASICS

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LTE Overview

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LTE key parameters Frequency Range Channel b d id h bandwidth, 1 Resource Block=180 kHz

UMTS FDD bands and UMTS TDD bands

1.4 MHz

3 MHz

5 MHz

10 MHz

15 MHz

20 MHz

6 RB 6 RB

15 RB 15 RB

25 RB 25 RB

50 RB 50 RB

75 RB 75 RB

100 RB 100 RB

Modulation Schemes

DL: OFDMA (Orthogonal Frequency Division Multiple Access) UL: SC‐FDMA (Single Carrier Frequency Division Multiple Access)

Multiple Access Multiple Access

DL: OFDMA (Orthogonal Frequency Division Multiple Access) DL: OFDMA (Orthogonal Frequency Division Multiple Access) UL: SC‐FDMA (Single Carrier Frequency Division Multiple Access)

MIMO technology

DL: Wide choice of MIMO configuration options for transmit diversity, spatial multiplexing, and cyclic delay diversity (max. 4 antennas at base station and handset) UL M lti UL: Multi user collaborative MIMO ll b ti MIMO

Peak Data Rate

DL: 150 Mbps (UE category 4, 2x2 MIMO, 20 MHz) 300 Mbps (UE category 5, 4x4 MIMO, 20 MHz) UL: 75 Mbps (20 MHz) p ( )

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

LTE Overview – Design Targets LTE Overview Design Targets and Multiple Access Technologies and Multiple Access Technologies

OFDM/OFDMA/SC‐FDMA

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LTE Overview

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

OFDM: Orthogonal Frequency Division Multi‐Carrier • LTE uses OFDM for the DL– that is, from the base station to q p the terminal. OFDM meets the LTE requirement for spectrum flexibility and enables cost‐efficient solutions for very wide carriers with high peak rates.

• The basic LTE downlink physical resource can be seen as a time‐frequency grid. In the frequency domain, the spacing b t between the subcarriers, Δf, is 15kHz. In addition, the OFDM th b i Δf i 15kH I dditi th OFDM symbol duration time is 1/Δf + cyclic prefix. The cyclic prefix is used to maintain orthogonality between the sub used to maintain orthogonality between the sub‐carriers carriers even even for a time‐dispersive radio channel.

Q , Q Q • One resource element carries QPSK, 16QAM or 64QAM. 25

LTE Overview

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OFDM – Cont.

Single Carrier Transmission O th Orthogonal lF Frequency Division Di i i M Multiplexing lti l i

OFDM signal generation is based on Inverse Fast Fourier Transform (IFFT) operation on transmitter side. side On receiver side side, an FFT operation will be used used.

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Pulse shaping and Spectrum • Two characteristics are important for a Signal:

Th titime d The domain i presentation t ti

– The time domain presentation: • It helps recognize “how long the symbol lasts on air”

Fourier Transform

– The frequency domain presentation: • to understand the required spectrum in terms of bandwidth 27

The frequency q y domain p presentation LTE Overview

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The rectangular Pulse

amplitude

• It is one of the most simple time‐domain pulses.

• It simply jumps at time t=0 to its maximum amplitude and It simply jumps at time t=0 to its maximum amplitude and after the pulse duration Ts just goes back to 0. fs =

Ts

1 Ts

FT Frequency Domain

Time Ti Domain time

IFT 28

LTE Overview

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Multi‐Path Propagation and Inter‐Symbol Interference

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LTE Overview

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Multi‐Path Propagation and Inter‐Symbol Interference • • • •

•

The cancellation of inter‐symbol interference makes more complex the hardware design of the receivers.

In WCDMA for instance the RAKE receiver requires a huge amount of DSP capacity.

One of the goals of future radio systems is to simplify receiver design One of the goals of future radio systems is to simplify receiver design.

Inter‐symbol interference originating from the pulse form itself is simply avoided by starting the next pulse only after the previous one finished completely, therefore introducing a Guard Period (Tg) after the Pulse. l l h f d d d( ) f h l There is no inter‐symbol interference between symbols as long as the multi‐path delay spread (e.g. delay difference between first and last p y p ( g y detectable path) is less than the guard period duration Tg.

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Multi-Path Propagation p g and the Guard Period 2 1

Time Domain

3

TSYMBOL

1

Tg Guard Period (GP)

TSYMBOL 2

time Guard Period (GP) TSYMBOL

ti time Guard Period (GP)

3

time 31

LTE Overview

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Multi-Path Propagation and the Guard Period 1

2 3

TSYM when the delay p of the spread multi-path environment is greater than the guard period duration (Tg), then we encounter inter-symbol interference (ISI)

4

Tg

1 time 2 time 3 time 4 time

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Reuse of the Guard Period • • •

•

There is the possibility to use the lost transmission time during the Guard Period by repeating part of the symbol during this period.

This is achieved by filling the guard period with either one or both of the following h h d b f ll h d d h h b h f h f ll two solutions: Cyclic Prefic (CP) and Cyclic Sufix (CS).

CP: The cyclic prefix is filling the final part of the guard period. It simply consists of the last part of the following symbol. Cyclic prefixes are used by all modern OFDM systems and their sizes range from 1/4 to 1/32 of a symbol period.

CS: The cyclic suffix fills the initial part of the guard period and it is simply occupied by the beginning part of the previous symbol.

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Cyclic Prefix •

•

In multi‐path propagation l h environments the delayed versions of the signal arrive with a time offset, so that the start of the symbol of the earliest path falls in the cyclic prefixes of the y p delayed symbols.

As the CP is simply a repetition of the end of the symbol this is not a the end of the symbol this is not a inter‐symbol interference and can be easily compensated by the f ll i d di b d following decoding based on discrete Fourier transform.

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LTE Overview

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Limitations of the Single‐Carrier Modulation • •

Using a single radio frequency carrier with rectangular pulse shaping has a major drawback: The cyclic prefix duration is fixed by the maximum expected delay spread over the multi‐path propagation models for the system. propagation models for the system

delaymax = TCP

•

•

•

The symbol duration can be made as small as the cyclic prefix size, but then only one half of th ti the time is used for data transmission, the other half is for the cyclic prefix, providing a very i df d t t i i th th h lf i f th li fi idi low efficiency (E) TSYMBOL E= TSYMBOL + TCP Also shorter symbol duration mean a broader spectrum bandwidth (fS) to be used for a Also shorter symbol duration mean a broader spectrum bandwidth (f ) to be used for a carrier.

1 1 fS = = TS TSYMBOL + TCP To increase efficiency the symbol duration must be made longer but then the symbol rate is To increase efficiency the symbol duration must be made longer, but then the symbol rate is reduced.

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Multi-Carrier Multi Carrier Modulation Subcarriers Guard Bands

011

001

011

100

101

001

Slow Data

011

101

frequency

Serial-to-Parallel Fast Data

Converter

011001011100101001011101

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Multi-Carrier Modulation –Cont.

The center frequencies must be spaced so that interference between different carriers, known as Adjacent Carrier Interference ACI, is minimized; but not too much spaced as the total bandwidth will be wasted.

Each carrier uses an upper and lower guard band to protect itself from its adjacent carriers. Nevertheless, there will always be some interference between the adjacent carriers. ∆fsubcarrier ∆fsub-used b d

f0

f1

f2

f3

fN

ACI = Adjacent Carrier Interference 37

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OFDM: Orthogonal Frequency Division Multi‐Carrier •

•

•

For the rectangular pulse there is h l l h a better option possible and it is even easier to implement.

We must just notice that the spectrum of a rectangular pulses shows null points exactly at shows null points exactly at integer multiples of the frequency given by the symbol duration. duration The only exception is the center frequency (peak power)

Single carrier

f/fs fs

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LTE Overview

fs

fs

fs

fs

fs

fs

fs

fs

fs

fs

fs

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

OFDM: Orthogonal Frequency Division Multi‐Carrier Thus OFDM simply places the next carrier exactly in the first null point of the Th OFDM i l l h i l i h fi ll i f h previous one.

With this we don’t need any pulse‐shaping.

B Between OFDM carriers using the OFDM i i h Orthogonal Subcarriers: it same symbol duration Ts, means that at the no guard bands are required. f s

subcarriers center frequencies, there is no Adjacent Carrier Interefence ((ACI))

Two carriers

f/fs 39

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ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Spectrum Overlapping of multiple OFDM carriers f n = f 0 + nf

s

= f0 + n

1 Ts

n = K − 1 , 0 ,1 , 2 . K

f0

f1

f2

f3

f4

No ACI (Adjacent Carrier Interference) 40

LTE Overview

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OFDM: Orthogonal Frequency Division Multi‐Carrier

Po ower Denssity

Power Den P nsity

OFDM allows a tight packing of small carrier ‐ called the subcarriers into a given frequency band.

Frequency (f/fs)

41

Saved Bandwidth

Frequency (f/fs)

LTE Overview

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The OFDM Signal

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OFDM and Multiple Access • Up to here we have only discussed simple point‐to‐ point or broadcast OFDM. point or broadcast OFDM. • Now we have to analyze how to handle access of multiple users simultaneously to the system each multiple users simultaneously to the system, each one using OFDM. • OFDM can be combined with several different OFDM b bi d ith l diff t methods to handle multi‐user systems: – Plain OFDM l – Time Division Multiple Access via OFDM – Orthogonal Frequency Division Multiple Access OFDMA 43

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Plain OFDM • Plain OFDM: Normal OFDM has no built‐in multiple‐ access mechanism access mechanism.

• This This is suitable for broadcast is suitable for broadcast systems like DVB‐T/H which transmit only broadcast and y multicast signals and do not really need an uplink feedback channel (although such systems exist too).

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Time Division Multiple Access via OFDM Time Division Multiple Access via i i i i li l i OFDM: The simplest model to implement multiple access handling is by putting a ti time multiplexing on top of OFDM. lti l i t f OFDM The disadvantage of this simple mechanism is, that every user gets the same amount of capacity (subcarriers) t f it ( b i ) and it is thus rather difficult to implement flexible (high and low) bit rate services. services Furthermore it is nearly impossible to handle highly variable traffic (e.g. web t ffi ) ffi i tl ith t t traffic) efficiently without too much h higher layer signaling and the resulting delay and signaling overhead.

1 UE 1 45

LTE Overview

2

UE 2

3

UE 3

common info

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Orthogonal Frequency Division Multiple Access OFDMA

Such block is simply a set of some subcarriers over some time. subcarriers over some time.

A single user can then use one or more Resource blocks.

1 UE 1

2 46

UE 2

3

UE 3

Orthogonal Frequency Multiple Access OFDMA

time ...

subccarrier

The basic idea is to assign subcarriers to h b i id i i b i users based on their bit rate services.

With this approach it is quite easy to h dl hi h d l bit t handle high and low bit rate users simultaneously in a single system.

But still it is difficult to run highly variable traffic efficiently traffic efficiently.

The solution to this problem is to assign to a single users so called resource blocks or scheduling blocks. or scheduling blocks

1 1 1 . .

1.

1 1 1 . .

RB 1.

1 1 1 . .

1.

2 2 2 . . .

1 3 3 3

1 3 3 3

1 3 3 3

3 3 3

2 2 2 . . .

... ... ...

... ...

3 ...

3 ...

3 ...

common info LTE Overview

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Difference between OFDM and OFDMA OFDM allocates users in time domain onlyy

47

OFDMA allocates users in time and frequency domain q y

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SC‐FDMA • •

•

• •

SC‐FDMA :Single Carrier Frequency Division Multiple Access SC‐FDMA is a new hybrid modulation scheme that cleverly combines the low PAR of single‐carrier systems with the multipath resistance and flexible subcarrier frequency allocation offered by OFDM. SC‐FDMA SC FDMA solves this problem by grouping together the resource blocks in solves this problem by grouping together the resource blocks in such a way that reduces the need for linearity, and so power consumption, in the power amplifier. A low PAPR also improves coverage and the cell‐ edge performance edge performance.

SC‐FDMA signal processing has some similarities with OFDMA signal processing, so parameterization of DL and UL can be harmonized.

SC‐FDMA is one option in WiMAX (802.16d) and it is the method selected for LTE in the uplink direction.

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Comparaison of CCDF of PAPR for IFDMA, LFDMA and OFDMA (a) :QPSK

(b) :16QAM

IFDMA = “Interleaved Interleaved FDMA” FDMA = Distributed SC-FDMA LFDMA = “Localized FDMA” = Localized SC-FDMA 49

localized mode (LFDMA) is used in LTE

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How does a SC‐FDMA signal look like?

• Similar to OFDM signal, but…

– in OFDMA, each sub‐carrier only carries information related to one specific y p symbol, – in SC‐FDMA, each sub‐carrier contains information of ALL transmitted symbols. y

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Comparing OFDMA & SC‐FDMA

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LTE Overview

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LTE downlink : conventional OFDMA

15 kHz

• LTE provides QPSK, 16QAM, 64QAM as downlink modulation schemes modulation schemes • Cyclic prefix is used as guard interval different interval, different configurations possible: – Normal cyclic prefix with 5.2 µs (first symbol) / 4.7 µs (other symbols) – Extended cyclic prefix with 16.7 µs Extended cyclic prefix with 16 7 µs

f0 f1 f2 f3 f4

52

• 15 kHz subcarrier spacing Scalable bandwidth • Scalable bandwidth www.cert.nat.tn

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OFDMA time‐frequency multiplexing

*TTI = transmission time interval ** For normal cyclic prefix duration 53

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spectrum flexibility • LTE physical layer supports any bandwidth from 1.4 MHz to 20 MHz in steps of MHz to 20 MHz in steps of 180 kHz (resource block) Current LTE specification • Current LTE specification supports a subset of 6 different system bandwidths • All UEs must support the maximum bandwidth of 20 MHz 54

Channel BW [MHz] Number of RBs

1.4

3

5

10

15

20

6

15

25

50

75

100

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Bandwidth Scalability SScalable bandwidth 1.4 – l bl b d idth 1 4 20 MHz using different number of subcarriers 20 MH i diff t b f b i Large bandwidth provides high data rates Small bandwidth allows simpler spectrum reframing, e.g. 450 MHz and 900 MHz

Bandwidth 1.4 MHz

Narrow Spectrum Reframing

3.0 MHz 5 MHz 10 MHz

High Data Rates

15 MHz 20 MHz

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LTE Frame Structure • LTE frames are 10 msec in duration. They are di id d i t 10 bf divided into 10 subframes, each subframe h bf being 1.0 msec long. Each subframe is further divided into two slots, each of 0.5 msec duration. Slots consist of either 6 or 7 ODFM symbols, depending on whether the normal or extended cyclic prefix is employed extended cyclic prefix is employed

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LTE Slot • The LTE Slot carries: – 7 symbols with short cyclic prefix b l h h l f – 6 symbols with long prefix

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OFDM Resource Block for LTE/EUTRAN • •

EUTRAN combines OFDM symbols in b b l so called resource blocks RB. A single resource block is always 12 g y consecutive subcarriers during one subframe (2 slots, 1 ms): – 12 subcarriers 12 subcarriers * 15 kHz= 180 kHz 15 kHz= 180 kHz

•

•

It is the task of the scheduler to assign resource blocks to physical channels belonging to different users or for general system tasks.

A single cell must have at least 6 g resource blocks (72 subcarriers) and up to 110 are possible (1320 subcarriers) subcarriers).

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LTE DL frame structure type 1 (FDD), DL # 00

# 01

# 02

# 03

# 04

# 05

# 06

# 07

# 08

# 09

# 10

# 11

# 12

# 13

# 14

# 15

# 16

# 17

# 18

# 19

1 slot = 0.5 ms 1 subframe = 1 ms

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LTE DL frame structure type 2 (TDD) 1 subframe = 1 ms 1 slot = 0.5 ms # 00

# 01

# 02

# 03

# 04

# 05

# 06

# 07

# 08

# 09

# 10

# 11

# 12

# 13

# 14

# 15

# 16

# 17

# 18

# 19

Special subframes containing: DwPTS: downlink pilot time slot UpPTS: uplink pilot time slot GP: guard period for TDD operation g Possible UL-DL configurations UL‐DL config 0 1 2 3 4 5 6

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0 D D D D D D

1 S S S S S S

Subframe number 2 3 4 5 6 U U U D S U D D D S U U U D D U U D D D U D D D D U U U D S

7 U U D D D U

8 U D D D D U

9 U D D D D D

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Modulation Schemes for LTE/EUTRAN •

• •

•

Each OFDM symbol even within a resource h b l h block can have a different modulation scheme.

EUTRAN defines the following options: QPSK, 16QAM, 64QAM. Not every physical channel will be allowed to Not every physical channel will be allowed to use any modulation scheme: Control channels to be using mainly QPSK. In general it is the scheduler that decides which form to use depending on carrier quality feedback information from the UE. q y

16QAM b0 b1b2b3 Im

1111

Re

QPSK b0 b1 Im 01

11

00

10Re

0000

64QAM b 0 b 1b 2b 3 b 4 b 5 Im

Re

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LTE Overview – Design Targets LTE Overview Design Targets and Multiple Access Technologies and Multiple Access Technologies

MIMO

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Multiple Antenna Techniques • •

•

•

MIMO employs multiple transmit and receive antennas to substantially enhance the air interface.

It uses space‐time coding of the same data stream mapped onto multiple transmit antennas, which is an improvement over traditional reception diversity schemes where only a single transmit antenna is deployed to y y g p y extend the coverage of the cell.

MIMO processing also exploits spatial multiplexing, allowing different data streams to be transmitted simultaneously from the different transmit streams to be transmitted simultaneously from the different transmit antennas, to increase the end‐user data rate and cell capacity.

In addition, when knowledge of the radio channel is available at the transmitter (e.g. via feedback information from the receiver), MIMO can also implement beam‐forming to further increase available data rates and p y spectrum efficiency 63

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Advanced Antenna Techniques • Single data stream / user • Beam‐forming Beam forming – Coverage, longer battery life

• Spatial Spatial Division Multiple Access Division Multiple Access (SDMA) – Multiple users in same radio resource

• Multiple data stream / user Diversity – Link robustness

• Spatial multiplexing – Spectral efficiency, high data rate support 64

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MIMO – Beamforming • Enhances signal reception through directional array gain, while individual antenna has while individual antenna has omni‐directional gain Extends cell coverage • Extends cell coverage • Suppresses interference in space domain p • Enhances system capacity • Prolongs battery life Prolongs battery life • Provides angular information for user trackingg 65

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LTE Overview – Design Targets LTE Overview Design Targets and Multiple Access Technologies and Multiple Access Technologies

AIR INTERFACE PROTOCOLS

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Radio Protocols Architecture • It is quite similar to the WCDMA protocol stack of UMTS. t k f UMTS • The protocol stack defines three layers: • the physical layer (layer 1) • data link and access layer (layer 2) d li k d l (l 2) • layer 3 (hosting the AS, the NAS control y ( g , protocols as well and the application level) 67

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Radio Protocol architecture‐ User plane UE

Header compression (ROHC) In‐sequence In sequence delivery of upper layer PDUs delivery of upper layer PDUs Duplicate elimination of lower layer SDUs Ciphering for user/control plane Integrity protection for control plane Timer based discard…

eNB PDCP

PDCP

RLC

RLC

MAC

MAC

PHY

PHY

AM, UM, TM ARQ (Re‐)segmentation Concatenation In‐sequence delivery Duplicate detection Duplicate detection SDU discard Re‐establishment…

Mapping between logical and transport channels (De)‐Multiplexing Scheduling information reporting Scheduling information reporting HARQ Priority handling Transport format selection…

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Control‐plane protocol stack Broadcast / Paging RRC connection setup Radio Bearer Control Mobility functions UE measurement control…

EPS bearer management Authentication ECM IDLE mobility handling ECM_IDLE mobility handling Paging origination in ECM_IDLE Security control…

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Physical Layer • • • • •

•

It provides the basic bit transmission functionality over air. the physical layer is driven by OFDMA in the downlink and SC‐FDMA in the uplink.

Physical channels are dynamically mapped to the available resources (physical resource blocks and antenna ports) (physical resource blocks and antenna ports).

To higher layers the physical layer offers its data transmission functionality via transport channels.

Like in UMTS a transport channel is a block oriented transmission service with certain characteristics regarding bit rates, delay, collision risk and reliability. y in contrast to 3G WCDMA or even 2G GSM there are no dedicated transport or physical channels anymore, as all resource mapping is dynamically driven by the scheduler dynamically driven by the scheduler.

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Medium Access Control (MAC) • • • • • •

MAC is the lowest layer 2 protocol.

Its main function is to drive the transport channels.

From higher layers MAC is fed with logical channels which are in one‐to‐ one correspondence with radio bearers.

Each logical channel is given a priority and MAC has to multiplex logical Each logical channel is given a priority and MAC has to multiplex logical channel data onto transport channels (demultiplexing in reception) Further functions of MAC will be collision handling and explicit UE identification.

An important function for the performance is the HARQ functionality which is official part of MAC and available for some transport channel which is official part of MAC and available for some transport channel types.

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Radio Link Control (RLC) • There is a one to one relationship between each Radio Bearer and each RLC instance • RLC can enhance the radio bearer with ARQ (Automatic Retransmission on reQuest) using sequence numbered data frames and status reports to trigger retransmission.

• The second functionality of RLC is the segmentation and reassembly that divides higher layer data or concatenates higher layer data into data chunks suitable for transport over transport channels which allow only a certain set of transport transport channels which allow only a certain set of transport block sizes.

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Layer 3 Radio Protocols •

PDCP (Packet Data Convergence Protocol) – Each radio bearer also uses one PDCP instance.

– PDCP is responsible for header compression (ROHC: RObust Header Compression; RFC 3095) and ciphering/deciphering.

– Obviously header compression makes sense for IP datagram's, but not for signaling.

Thus the PDCP entities for signaling radio bearers will usually do ciphering/deciphering Thus the PDCP entities for signaling radio bearers will usually do ciphering/deciphering only.

•

RRC (Radio Resource Control) – RRC is the access stratum specific control protocol for EUTRAN. h f l lf – It will provide the required messages for channel management, measurement control and reporting, etc.

•

NAS Protocols l – The NAS protocol is running between UE and MME and thus must be transparently transferred via EUTRAN. – It sits on top of RRC, which provides the required carrier messages for NAS transfer 73

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Layer 1/2 Radio Protocols – Summary

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RRC Protocol

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LTE MBMS Concept • •

• •

•

MBMS (Multimedia Broadcast Multicast Services) is an essential requirement for LTE. The so‐called E‐MBMS will therefore be an integral part of LTE. In LTE, MBMS transmissions may be performed as single‐cell transmission or as b f d l ll multi‐cell transmission. In case of multi‐cell transmission the cells and content are synchronized to enable for the terminal to soft‐combine the energy from multiple t transmissions. i i The superimposed signal looks like multipath to the terminal. This concept is also known as Single Frequency Network (SFN).

The E‐UTRAN can configure which cells are part of an SFN for transmission of an MBMS service. The MBMS traffic can share the same carrier with the unicast traffic or be sent on a separate carrier.

For MBMS traffic, an extended cyclic prefix is provided. In case of subframes carrying MBMS SFN data, specific reference signals are used. MBMS data is carried on the MBMS traffic channel (MTCH) as logical channel.

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LTE vs WiMAX − Both are designed to move data rather than voice and both are IP networks based on OFDM technology. − WiMax is based on a IEEE standard (802.16), and like that other popular IEEE effort, b d d d( ) dlk h h l ff Wi‐Fi, it’s an open standard that was debated by a large community of engineers before getting ratified. The level of openness means WiMax equipment is standard and therefore cheaper to buy. d th f h t b − As for speeds, LTE will is faster than the current generation of WiMax. − However, LTE will take time to roll out, with deployments reaching mass adoption by 2012 . WiMax is out now, and more networks should be available later this year. − The crucial difference is that, unlike WiMAX, which requires a new network to be built, LTE runs on an evolution of the existing UMTS infrastructure already used by over 80 per cent of mobile subscribers globally. This means that even though development and deployment of the LTE standard may lag Mobile WiMAX, it has a crucial incumbent advantage.

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Summary • The 3GPP Long Term Evolution (LTE) represents a major gy advance in cellular technology.

• LTE is designed to meet carrier needs for high‐speed data and media transport as well as high‐capacity voice support well into the next decade.

• LTE is well positioned to meet the requirements of next‐ generation mobile networks. It will enable operators to offer high performance, mass‐market mobile broadband services, through a combination of high bit rates and system through a combination of high bit‐rates and system throughput – in both the uplink and downlink – with low y latency.

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Summary– Cont.

• LTE infrastructure is designed to be as simple as possible to p y p , g gy deploy and operate, through flexible technology that can be deployed in a wide variety of frequency bands.

• LTE offers scalable bandwidths, from from 1.4 MHz up to 20MHz, together with support for both FDD paired and TDD unpaired spectrum.

• The LTE–SAE architecture reduces the number of nodes, supports flexible network configurations and provides a high level of service availability level of service availability.

• Furthermore, LTE–SAE will interoperate with GSM, WCDMA/HSPA TD‐SCDMA WCDMA/HSPA, TD SCDMA and CDMA. and CDMA www.cert.nat.tn LTE Overview 79

ITU/BDT Arab Regional Workshop on “4G Wireless Systems” – Tunisia 2010

Summary – Cont.

Technologies/Features

Benefits

OFDMA with CP/SC‐FDMA with CP

+ Equalizer simpler Scheduling time/frequency Better PAPR (SC PAPR (SC‐FDMA) FDMA) ISI suppression (CP)

QPSK, 16 QAM, 64 QAM

+ Higher bitrates Adaptative p modulation

Canaux communs

+ Variable traffic Better capacity

TTI = 1 ms TTI = 1 ms

+ Better response to channel to channel variation Higher bitrates

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LTE Overview

Requirements

‐ Scheduling is needed

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Summary– Cont.

Technologies/Features

Benefits

TTI = 1 ms

Better response to channel + variation Higher bitrates

Flat architecture

+

Simpler Architecture Better latency

All IP All IP

+

Architecture simpler p Convergence

MIMO

+ Higher bitrates

Bande passante flexible(1.4 Æ Bande passante flexible(1 4 Æ 20 20 MHz)

+

Universal frequency reuse (1/1)

+ Better spectral efficiency

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LTE Overview

Schedulingg with priorities is needed

ICIC

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Thank you for your for your Attention

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